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Thread: River Punt - Opinions?

  1. #1
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    Default River Punt - Opinions?

    Hi Guys & Gals,

    I've been lurking around on this forum for a while (since I decided to build myself a river boat.)

    Take a look at these photos of a 18' Punt built in 1981:

    Particulars:
    1) 18' AOL x 5' Beam
    2) 48" wide & 3/16" thick bottom (dead flat for first 12')
    3) Sides are 1/8", empty weight of the boat/motor is 875-900lbs
    4) There are 3x 2" channel runners on the bottom. (properly cut-away for unobstructed flow to the pump)

    Observations:
    1) With the E-tec 50hp this punt will get on step with 2 guys and a moose aboard... By our standards, this is enough power. As a matter of fact, the fellow who owns this boat used to run a Evinrude "Commercial 45" (with jet) for many years, and still has that set-up on a second identical skiff.
    2) When running in a riffle or small chop the motor can/will start cavitating.
    3) Draws a little too much water when stopped (sucks up gravel when pulling out of the hole)

    I would like to build a similar punt with the following "improvements"

    1) 60" wide bottom with 3deg of "V"
    2) 18" longer (may as well use up the whole sheet of aluminium lol.)
    3) Shallow jet tunnel to get pump out of the riverbed.

    Soliciting Opinions...
    1) Will the 3deg of "V" be enough to help with the cavitation issues?

    2) I've bought one of the new Merc 60/40 jets... When looking at the pump/impellor specs; I see it runs a 6 7/8" impellor in the "large" bowl size verses the E-tec's 6 1/8" in the "medium" bowl. I've made the assumption that the Merc should have a little better torque for getting out of the hole... Tell me I'm right.! lol

    Cheers, Sam

    Goggle-Earth the Kliniklini River (Knight Inlet, BC)
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  2. #2
    Member Akgramps's Avatar
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    3 degrees is still fairly flat, my current boat is a 60" wide (bottom) w/tunnel and 6 degree deadrise. generally does not have much of a problem w/cavitation under most operating conditions. However in a heavier chop, such as some parts of the copper river I can get some cavitation. Many manufacturers seem to be use 9 degrees or more. I doubt a few extra degrees of deadrise will have much impact on shallow running, particuarliy in a relatively light boat. What is in front of the tunnel is very important, things such as lifting strakes or keel. Hope this helps
    “Nothing worth doing is easy”
    TR

  3. #3
    Member SusitnaAk's Avatar
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    Default pic,s

    Maybe it,s the angle of the picture #2 But that motor there looks like it hanging down there about a foot past the bottem of the boat?To far.. Might be the reason it draws to much water and sucking up rocks,Cavitaion has a lot to do with the set up of the motor to the bottem of boat,and the angle the jet foot is to the water, I always had a bit of slipage in the waves, They used to have these little wing looking things went on either side of the jet foot helped out. Also some ran a pc,s of metal/umhw, from back boat to the jet to keep the water there, All but deep 2-3ft waves, I used to run a ruler along the bottem of the boat and have it meet the leading edge of the jet,start from there, Take out for a run, doing hard turns and such, Moving up one hole at a time, til i got it to cavitate, on a hard turn, then move it back down one hole and bolt in place and call that the sweet spot.

  4. #4
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    The jet is set up properly. I would say that for a flat bottom boat you could not do much better... Just wondering how much deadrise is enough to actually make a difference in aerated water. We would like to improve the performance without sacrificing the ability to run shallow. Although these skiff's are not fast, they have enough flat surface area to go fairly skinny. Introducing a V into the hull and running a tunnel would save the foot a lot of abuse. As for getting out of the hole, I'm talking about in water shallow enough for the chines to touch when rocking the boat.

  5. #5
    Member SusitnaAk's Avatar
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    I see, the picture first glance made it look like the boat was resting on the Jet! Ha, bifocals are a pain arse. I like the tunnel Idea, The more V the lower its going to sit... On step wouldn,t know if make much difference. Ive seen poeple up here run jets on Lunds, vbottem, boats and do well.Good luck with your project let us know what you come up with..

  6. #6
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    Well I drew up a set of lines and pulled the offsets for a new version of the local river skiffs. Took them over to a fellow well versed in AutoCad... Here are a couple of the first renderings.

    I went with 4 degrees of deadrise aft. AUW of the hull is looking to be 820lbs. This seamed heavy, so we weighed the skiff in the earlier photos... 1050lbs (with the engine) is the actual, so we are not too far off the earlier design.
    Air tanks will be incorporated to provide approximately 1500lbs of positive bouancy beyond boat/motor... We should be able throw a quad in the bow, pull the transom plug and have the boat settle half way to the gunnel.
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  7. #7

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    Hi

    just saw your post, and thought I'd add my .02. I have a Mercury 60/40 and a boat that's shorter and wider than what you are planning, but probably close to the same weight. If I were in your shoes, and had bought the motor already, the most important variable I'd consider in building the boat is weight. Have a look at the horsepower/weight chart at www.outboardjets.com and see how much you can get away with for that motor. Lighter is better. My rig weighs in at about 1200 w/ motor and it's not near as responsive as I'd like it to be.

    second thing I'd say is be very cautious in adding a tunnel to the boat. Mine was designed according to the specs on the site above and other than running shallow, I can't think of any other benefits. The boat sits quite low in the water, doesn't slide, and cavitates/falls off step in hard corners.

    good luck with it!

  8. #8
    Member MARV1's Avatar
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    Nice looking design.
    The emphasis is on accuracy, not power!

  9. #9
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    Default Lets get started.

    Finally found some time to get going on the project.
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    Waterjet-cut parts.
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  11. #11
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    Hmm, looks like not too much interest in backyard projects around here... But I post anyway.

    River Punt - Jig (25).jpgRiver Punt - Construction (5).jpg

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  14. #14
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    Initial motor set-up before flipping the boat (for final welding of seams and external longitudinal framing.)
    River Punt - Construction (70).jpgRiver Punt - Construction (53).jpg

  15. #15
    Moderator stid2677's Avatar
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    Looks nice to me. The jig alone was quite a build. Look forward to your run report.


    Steve
    "I refuse to let the things I can't do stop me from doing the things I can"
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    http://www.residenthuntersofalaska.org/

  16. #16
    Moderator bkmail's Avatar
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    Nice looking ride. Look forward to more pics and the result. Keep the photos coming. I wish I had the welding talent to build my own ride.
    BK

  17. #17
    Member spoiled one's Avatar
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    Very cool project. Check your pms.


    Guess you are not set up for pms? You might try and posting your build here: Aluminum Alloy Boats

    There have been some similar projects.
    Spending my kids' inheritance with them, one adventure at a time.

  18. #18
    Member broncoformudv's Avatar
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    I like the looks of your build and agree with stid2677 the jig alone was one heck of a build can't wait to see the finished product. What made you go with the air bladders? Looks like they take up a lot of space inside your hull.

    You might be able to find some similar threads on the old riverjet magazine forum. I seem to recall a guy in Cali building a boat a little smaller than yours with an inboard and I am sure there were more on there than that.

  19. #19
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    "The jig alone was quite a build" Yes, I have 30hrs into the jig.

  20. #20
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    Simple task to roll the boat over when supported on the CG.
    River Punt - Construction (82).jpg

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